Windows – Outlook 2010 automatically filling in the wrong username and not remembering passwords

This blog entry provides a solution:

Get Outlook 2003 RPC Over HTTP To Remember Your Password

On your client, you need to go into your Mail settings, then check your Exchange Proxy Settings.

• Ensure that Connect using SSL only and Mutually authenticate the session when connecting with SSL are both checked on.
• Enter in the Principal name for proxy server: in the msstd:frontend.domain.com format.
• Select both the Fast and Slow settings.
• Make sure the Proxy authentication settings is set to NTLM Authentication.

Now the real trick. Outlook will, when you select Remember my Password, store your password for the Back-end Mailbox server. But it does not save your password for the Front-end Proxy server.

• Go into your Control Panel > User Accounts > Advanced > Manage Passwords.
• Click Add, then type out the name of your Front-end server. This should be the same name as your SSL certificate on the default web site that contains the RPC virtual directory, put in your username and password.

It's for Outlook 2003, but I guess it should work for Outlook 2007 too.

It's actually more an Active Directory issue than an Exchange one.

Both DOMAIN\USERNAME and USERNAME@DOMAIN are functionally the same for Windows.

So unless the email domain is the same as the Windows domain, by default, USER@EMAILDOMAIN.COM will not work to log the user in.

That being said, you CAN do a work around by adding the email domain as a UPN suffix in Active Directory, then changing the user's UPN suffix to match email. That's generally only done in Hosted Exchange environments with separate GALs, mainly because the UPN suffix can then cause issues accessing domain resources, if the user is prompted to authenticate manually.

tl;dr - if it's only one user, I'd probably just have them authenticate as user@windowsdomain.com. If the user is important, there is a workaround, and I can walk you through those steps, but it can cause other issues.